The present invention relates to a chuck. More particularly this invention concerns a multiple-jaw lathe chuck for rotating a workpiece during a machining operation.
A standard lathe chuck has a chuck body centered on and rotatable about a main axis and formed with a plurality of radially extending jaw-guide grooves and, transverse to the grooves, with respective guide passages. Respective jaws radially. displaceable in the grooves each have an array of teeth exposed in the respective guide passage and respective control rods displaceable along the passages each also have an array of teeth meshing with the teeth of the respective jaw. These teeth are angled relative to the respective passages such that movement of the rods along the respective passages displaces the respective jaws radially in their guide grooves. Sides of the control rods are formed with angled grooves in which engage parts of an axially displaceable piston that is moved in one direction to shift the control rods in one direction and spread the jaws, and in the opposite direction to oppositely shift the control rods and bring the jaws together. Normally each control rod is associated with a respective adjuster that allows it to be moved so that a new jaw can be loaded into the respective slot.
A problem with such chucks is that, when holding a very large workpiece, the jaws are only engaged together by one tooth. Furthermore it is possible for the jaw to completely disengage and fly radially off, in particular if during a high-speed machining operation of such a large-diameter workpiece the engaged teeth on the jaw or rod shear off. Dring normal refitting of the chucks when the control piston that actually operates the rods is pulled back out of engagement with the control rods, these control rods can shake loose into positions where they interfere with installation of fresh jaws.
It is therefore an object of the present invention to provide an improved lathe chuck.
Another object is the provision of such an improved lathe chuck which overcomes the above-given disadvantages, that is which ensures that the control rods will not come loose or get in the way when new jaws are being fitted.
A lathe chuck has according to the invention a chuck body centered on and rotatable about a main axis and formed with a plurality of radially extending jaw-guide grooves and, transverse to the grooves, with respective guide passages each in turn formed with an abutment. Respective jaws displaceable in the grooves each have at least one tooth exposed in the respective guide passage and respective control rods displaceable along the passages each have at least one tooth meshing with the tooth of the respective jaw. The teeth are angled relative to the respective passages such that movement of the rods along the respective passages displaces the respective jaws radially in their guide grooves. In accordance with the invention a control pin is axially displaceable in each rod between an extended position projecting into the respective jaw-guide groove and a retracted position. The control pins are displaced on engagement with the teeth of the respective jaws. into the retracted positions. A latch pin is axially displaceable in each rod between an extended latching position engaging the respective abutment and preventing movement of the respective rod in the respective passage and a retracted position permitting such movement. A spring urges the pins into their extended positions, and a coupling member engaged between the pins displaces the respective latch pin into the respective retracted position on displacement of the control pin into its retracted position. Thus, when there is no jaw in the guide groove, the latch pin of the respective control rod latches same against movement in the respective passage.
With this system, therefore, if a jaw is not properly fitted to a guide groove, the respective control rod will remain locked in an end position, precluding use of the chuck until the missing or misfitted jaw is attended to. A jaw can only be inserted into its guide groove when the respective control rod is fully retracted out of the way; otherwise the control rod will block the guide groove and prohibit sliding-in a jaw and will simultaneously block actuation of the jaw-tightening chuck piston.
According to the invention each rod has an end position with the respective tooth outside the respective jaw-guide groove and unengageable with a jaw therein. The chuck further has a respective resetting element in each rod and engageable with the chuck body and with the respective latch pin in the end position of the respective rod for holding the respective latch pin in the respective retracted position. Thus the control rods are only latched in place when they are not in their end positions or their control rods are not in engagement with the respective jaw. If a jaw has been improperly loaded so that its teeth are not caught on the teeth of the respective control rod, it will be necessary to back off the control rod and reset the jaw before the chuck can be tightened. To this end the rods are each closely juxtaposed with an end of the respective passage in the end position and each rod is formed with an element guide slidably receiving the respective resetting element and open axially toward the end of the respective passage.
The chuck further has according to the invention respective springs urging the resetting elements into a position out of engagement with the respective latch pins and projecting axially from the respective control rods toward the end of the respective passage. The resetting elements are engageable with the ends of the respective passages and pressable thereby into engagement with the respective latch pins to displace same into the respective retracted positions.
Each resetting rod has a flat face lying flatly against and slidable on a respective flat race of the respective passage. In addition each resetting rod and the respective latch pin have respective angled camming faces engageable with each other.
Each control member in accordance with the invention is a two-arm lever pivoted in the respective rod and having one end engaging the respective control pin and an opposite end engaging the respective latch pin. Alternately, the control and latch pins have confronting toothed edges and the control members are gear wheels rotatably mounted in the respective rods and meshing with the toothed edges of the respective pins. In either case each control rod is provided with an axle on which the respective control member is rotatable.
Furthermore according to the invention each rod is formed with an actuating groove having an end portion extending parallel to the respective passage and a main portion extending at an angle to the respective passage. The chuck further has according to the invention an actuating element having respective parts engaged in the actuating grooves. The element is axially displaceable to shift the rods in the respective passages when the parts are engaged in the main portions but is axially locked when any of the parts is in the respective end portion.
Normally the actuating element is a piston that is shifted axially to move all the jaws simultaneously. An end-position switch prevents the drive that rotates the chuck about its axis from starting unless the piston is moved out of an end position indicating that the jaws have been tightened on the workpiece. With the system of this invention this piston will hang up in the end portions of the grooves, making it impossible for the piston to retract and for the drive to start. It becomes necessary for the machine operator to determine which jaw is not properly set and fix it before the machine can be restarted.